Recent anatomical findings in animal models suggest that defects in photoreceptor renewal mechanisms may play a fundamental role in the etiology of hereditary retinal degenerations. Studies are proposed that will evaluate diurnal variations in rod and cone electroretinograms (ERGs) as functional correlates of rod and cone renewal in the human retina. These studies will determine the precise relationship between diurnal variations which have been documented in the ERG and daily light cycle as well as evaluate variations in quantal absorption and other factors that may underlie the diurnal rhythm. Studies of the diurnal rhythm in young patients with retinitis pigmentosa will evaluate possible defects in mechanisms of photoreceptor renewal. Studies during long-term monocular occlusion in normal subjects and patients with retinitis pigmentosa will assess progressive alterations of the rod ERG in darkness, reflecting a shift in the balance between rates of disc shedding and disc renewal. Prospective studies, using recently developed preferential-looking and pupillometric procedures, will document early reductions in acuity and rod sensitivity in infants and toddlers with retinitis pigmentosa and allied retinal degenerations. Results from these studies will help distinguish congenital stationary defects from early onset diseases and help identify impairments which may be amenable to early treatment. Focal cone ERGs and psychophysical measures of cone directional sensitivity will be applied to the study of acquired macular disorders. The Stiles-Crawford technique coupled with selective adaptation is proposed as a paradigm for obtaining independent measures of cone optical bandwidth and cone disarray. The sensitivity of this paradigm will be evaluated initially by utilizing the known variations in cone structure across the normal retina and, secondly, by studying abnormal cone alignment in patients with known tractional forces acting on the retina. Measures of cone optical bandwidth and cone disarray in patients with macular disease will allow us to assess the role of each factor. Prospective studies of the focal cone ERG and cone directional sensitivity in patients with unilateral macular degeneration will determine whether defects in cone function precede clinical lesions in at-risk eyes and provide data on the developmental course of functional deficits.